Processors, memory devices, field-emission-displays, read/write heads and other microelectronic devices generally have integrated circuits with microelectronic components. A large number of individual microelectronic devices are generally formed on a semiconductor wafer, a glass substrate, or another type microelectronic workpiece. In a typical fabrication process, one or more layers of metal are formed on the workpieces at various stages of fabricating the microelectronic devices to provide material for constructing interconnects between various components.
The metal layers can be applied to the workpieces using several techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced deposition processes, electroplating, and electroless plating. The particular technique for applying a metal to a workpiece is a function of the particular type of metal, the structure that is being formed on the workpiece, and several other processing parameters. For example, CVD and PVD techniques are often used to deposit aluminum, nickel, tungsten, solder, platinum and other metals. Electroplating and electroless plating techniques can be used deposit copper, solder, permalloy, gold, silver, platinum and other metals. Electroplating and electroless plating can be used to form blanket layers and patterned layers. In recent years, processes for plating copper have become increasingly important in fabricating microelectronic devices because copper interconnects provide several advantages compared to aluminum and tungsten for high-performance microelectronic devices.
Electroplating is typically performed by forming a thin seed-layer of metal on a front surface of a microelectronic workpiece, and then using the seed-layer as a cathode to plate a metal layer onto the workpiece. The seed-layer can be formed using PVD or CVD processes. The seed-layer is generally formed on a topographical surface having vias, trenches, and/or other features, and the seed-layer is generally approximately 1000 angstroms thick. The metal layer is then plated onto the seed-layer using an electroplating technique to a thickness of approximately 6,000 to 15,000 angstroms. As the size of interconnects and other microelectronic components decrease, it is becoming increasingly important that a plated metal layer (a) has a uniform thickness across the workpiece, (b) completely fills the vias/trenches, and (c) has an adequate grain size.
Electroplating machines for use in manufacturing microelectronic devices often have a number of single-wafer electroplating chambers. A typical chamber includes a container for holding an electroplating solution, an anode in the container to contact the electroplating solution, and a support mechanism having a contact assembly with electrical contacts that engage the seed-layer. The electrical contacts are coupled to a power supply to apply a voltage to the seed-layer. In operation, the front surface of the workpiece is immersed in the electroplating solution so that the anode and the seed-layer establish an electrical field that causes metal in a diffusion layer at the front surface of the workpiece to plate onto the seed-layer.
The structure of the contact assembly can significantly influence the uniformity of the plated metal layer because the plating rate across the surface of the microelectronic workpiece is influenced by the distribution of the current (the “current density”) across the seed-layer. One factor that affects the current density is the distribution of the electrical contacts around the perimeter of the workpiece. In general, a large number of discrete electrical contacts should contact the seed-layer proximate to the perimeter of the workpiece to provide a uniform distribution of current around the perimeter of the workpiece. Another factor that affects the current density is the formation of oxides on the seed-layer. Oxides are generally resistive, and thus oxides reduce the efficacy of the electrical connection between the contacts and the seed-layer. Still other factors that can influence the current density are (a) galvanic etching between the contacts and the seed-layer, (b) plating on the contacts during a plating cycle, (c) gas bubbles on the seed-layer, and (d) other aspects of electroplating that affect the quality of the connection between the contacts and the seed-layer or the fluid dynamics at the surface of the workpiece. The design of the contact assembly should address these factors to consistently provide a uniform current density across the workpiece.
One type of contact assembly is a “dry-contact” assembly having a plurality of electrical contacts that are sealed from the electroplating solution. For example, U.S. Pat. No. 5,227,041 issued to Brogden et al. discloses a dry contact electroplating structure having a base member for immersion into an electroplating solution, a seal ring positioned adjacent to an aperture in the base member, a plurality of contacts arranged in a circle around the seal ring, and a lid that attaches to the base member. In operation, a workpiece is placed in the base member so that the front face of the workpiece engages the contacts and the seal ring. When the front face of the workpiece is immersed in the electroplating solution, the seal ring prevents the electroplating solution from contacting the contacts inside the base member. One manufacturing concern of dry-contact assemblies is that galvanic etching occurs between the contacts and the seed-layer when an electrolyte solution gets into the dry contact area. Galvanic etching removes the seed-layer at the interface of the contacts, which can cause a non-uniform current distribution around the perimeter of the workpiece. Therefore, even though dry-contact assemblies keep the contacts clean, they may produce non-uniform metal layers on the workpieces.
Another type of contact assembly is a “wet-contact” assembly having a plurality of electrical contacts that are exposed to the electroplating solution during a plating cycle. Because the contacts are exposed to the electroplating solution during a plating cycle, the metal in the electroplating solution also plates onto the contacts. The contacts, however, may plate at different rates such that some contacts can have a greater surface area of conductive material contacting the seed-layer. The in-situ plating of contacts can accordingly reduce the uniformity of the metal layer on the workpiece. Additionally, wet-contact assemblies must be periodically “de-plated” to remove the metal that plates onto the contacts during a plating cycle. Therefore, it would be desirable to develop a wet-contact assembly that eliminates or reduces the processing concerns associated with exposing the contacts to the electroplating solution.